A chain of bivalue cells; the common candidate at both ends can be eliminated from cells seeing both ends.
A chain formed by bivalue cells connected through shared candidates. The candidate common to both ends of the chain can be eliminated from any cell seeing both endpoints.
This is the generalization of XY-Wing: an XY-Wing is simply a 3-cell XY-Chain. Longer chains are more powerful but harder to find.
34 | 34 | 9 | 7 | 1 | 5 | 6 | 2 | 8 |
| 1 | 25 | 25 | 6 | 8 | 9 | 3 | 4 | 7 |
68 | 67 | 678 | 2 | 3 | 4 | 1 | 5 | 9 |
26 | 26 | 1 | 5 | 7 | 3 | 8 | 9 | 4 |
358 | 35 | 358 | 4 | 9 | 6 | 2 | 7 | 1 |
| 7 | 9 | 4 | 1 | 2 | 8 | 5 | 3 | 6 |
24 | 8 | 27 | 9 | 5 | 1 | 47 | 6 | 3 |
56 | 1 | 56 | 3 | 4 | 7 | 9 | 8 | 2 |
| 9 | 347 | 37 | 8 | 6 | 2 | 47 | 1 | 5 |
This 9×9 puzzle is solver-verified to require this technique on its solution path.